Helium space discharge tube



March 6, 1928. 1,661,436

F. S. M CULLOUGH HELIUM SPACE DISCHARGE. TUBE Filed April 5. 1924 Z INVENTOR r tube of the hot cathode type, wherein helium Patented Mar. 6, 1928,

FREDERICK S. KOGULLOUGH, OI WILKINSBUBG, PENNSYLVANIA srnqn msonanqn roan.

, Applicatlonfiflled April 8, 1m. Serial in. 703,021,

This invention is for a" space discharge is present between the cathode and theanode of the tube, and for a method of making the same.

It is well known inthe art. that space discharge tubes that are evacuated vto an extremely high degree have very marked characteristics differing from the so-called gaseous tubes wherein the gaseouscondition is produced either by'failure to evacuate the tube to an extremely high degree, or by restoring to the highly evacuated tube an inert gas from an external supply.

Due to the greater stability of the highly evacuated tubes, or hard tubes, over the gaseous or soft tubes, the former have generally been preferred.

I have discovered, however, that, if helium can be produced in the tube after the tube has been thoroughly de-gasitied by the usual methods of heating and evacuation on the.

pump, and the tube sealed oiffvery satisfactory and highly eflicient results may be obtained, and this with a very low temperatu-re on the cathode.

According to the present invention, I propose to provide in the tube a cathode capable of producing or liberating helium gas,

in sufiicient quantities .to lower theimpedance across the space between the cathode and the anode, but insufiicient to render the tube unstable in the manner that the soj is appliedto the filament which is gradually also comprises the anode of the tube;

In the drawings, 5 designatesa metal envelope which also comprises an anode for thetube; 6 is a lass sealsecured thereto; 7 is a cathode or 4 ament supported-byand id. At 10 is designated the .point where t e tube is evacuate and eventually sealed 0 v The cathode 7 comprises a'metal base or wire preferably formed of molybdenumon joined to connectors 8; and 9 designates thewhich is a coating of thoriumnitr'ate or' uranium nitrate, .This coating may be ap- After being heated a for a suflicient period of time,-the tube may subsequently be sealed ofi.

plied by alternately dipping the-wire base in a thorium nitrate or uranium nitrate solution and drying the coating until the coating is sufficiently he'avy.

This filament is then assembled in the tube, and the tube placed on the pump for evacuation. After a preliminary exhaustion, an oven is lowered around the entire tube and the tube baked at a fairly higli degree of temperature, but below the melting point of the glass. While the tube continues on the pump, a heating coil a is placed around the metal part of the tube only, and the temperature of the metal raised toabout 800 degrees or 1000 degrees C., by means of which the metal shell is de-gasified, This heating of the shell also heats the cathode, to substantially the same temperature. This heating of the cathode in a high vacuum from an external source is very important;

in that it conditions or activates the filament, and brings it toa'state Where it will properly function in the tube and resist.

suflicient period to drive out all helium that may be evolved.

with the external coil After sealing the tube, a very low current increased until the filamentbecomes hot,

perhaps to a dull red heat. The tube, which has been extremely hard, due to the de-gasitying process, is allowed to age for a while- With the current applied to the filament.

After a comparatively short-period of time,

helium will be found to be present in the tube. .This probably results from atomic nitrate under proper conditions has long been, known to chemists and the present inpbhenomenon to advant vention utilizes this age in an electron tu The vquantity of helium evolved is, of

course, very minute, but isamply sufficient to lower the impedance fromthe-cathode to.

the anode, so that the tube will function with- I a ver low heating current in the filament,

and elium will assist in cooling the tube.v

Upon reaching a certainstage, the evolution of helium apparently ceases, a state of equilibrium apparently being reached.

It further appears that the tube is quite distinctly more satisfactory than the usual gaseous tubes having an appreciable residuum of atmospheric gases therein or having an inert gas restored thereto from an external supply. This may perhaps be due to the fact that the helium evolved from the cathode returns into more intimate contact therewith than would gas supplied to the tube from an external source. This would seem to be borne out by a spectroscopic inspection, wherein the greatest manifestation of helium is apparent in immediate proximity to the cathode, although such manifestation may be due also to the greater atomieal or molecular activity of the gas in the vicinity of the cathode by reason of the cathode bein hot.

\atever the theory as to the presence and distribution of the evolved helium may be, the practical result is that an exceptionally efficient tube is provided by its presence, and that this tube can be operated at very low temperatures comparatively, so that it is very desirable, particularly in power tube work where the question of dissipating the heat energy of the cathode is a serious problem, and is very suitable for tubes having an exterior air cooled metallic anode. 4

I claim as my invention:

1. The method of making a space discharge tube having helium thcrein which conslsts in assembling a tube having an anode and a cathode on which latter there is a substance ca )able of liberating helium when heated exiausting and de-gasifying the anode and the cathode by exhaustion and baking, sealing off the tube, and applying- FREDERICK S. MCCULLOUGH. 

